The only valid reason for downloading I know of is that some (but not all) GI style mags can be near impossible to seat with a closed bolt. I have also seen the floorplate blow off some fully loaded 30-rounders with a little rough treatment but who knows what really caused it to happen? It seems to me some GI mags have a little more substantial "ears" securing the floorplate than others. For mine that I have kept loaded I prefer PMags & use the feed ramp clip designed to relieve the pressure. I have read that Magpul has maintained fully loaded mags since they were first introduced and they still remain perfect today. They are also made with a smidgen of extra room to facilitate loading a full mag with a closed bolt.